Field of the Invention
The present invention relates to a fired precast block to be used as part of an inner lining layer of a blast furnace runner, a blast furnace, etc.
Description of the Related Art
Blast furnace runners are equipment for separating hot liquid (molten metal and slag) drained from a tap hole of a blast furnace and having high temperatures of 1,450 to 1,550 deg. C. into molten metal and molten slag by utilizing a difference in specific gravity, and transporting the molten metal and the molten slag to subsequent transport vessels or other facilities, respectively. A refractory material (a wear lining) of portions of a blast furnace runner to contact the molten metal or slag is easily worn away by molten slag. Therefore, it is demanded that the wear lining has high heat resistance and corrosion resistance.
In general, a blast furnace runner is produced by pouring an unshaped material (a castable) comprising alumina, magnesium spinel, silicon carbide, etc. as aggregate in formwork and thus forming a passage for molten metal or slag. A wear lining of the blast furnace runner is supported by an iron shell constituting an outer frame by way of refractories such as alumina-silicon carbide bricks and a heat-insulating castable.
Of the hot liquid, molten metal is metal in a liquid state having iron as a main component, and molten slag is oxides such as SiO2, Al2O3 and CaO in a liquid state. The molten metal and the molten slag are different in specific gravity and the molten metal has a greater specific gravity than the molten slag. Therefore, the molten metal descends to and flows at a bottom of a blast furnace runner, while the molten slag floats on top of the molten metal. It should be noted that an interface between the molten metal and the molten slag is called metal line and an interface between the molten slag and the air is called slag line. A portion of a side wall of a blast furnace runner to contact the metal line is called a metal line portion, and a portion of a side wall of a blast furnace runner to contact the slag line is called a slag line portion.
A wear lining is susceptible to cracking and local damages because the wear lining is brought in contact with high-temperature molten metal or slag and subjected to repetition of heating and cooling. Particularly severe wear is observed on the wear lining at a portion of a side wall to contact a boundary surface of molten slag or metal, such as the abovementioned slag line portion and the abovementioned metal line portion, because local flows of the molten slag or metal occur. If wear of the wear lining increases and thus thickness of the remaining side wall decreases, there arises a risk that molten metal or slag may leak out. Leak of molten metal or slag not only causes trouble to attached facilities of the blast furnace but also exerts adverse effect on operation safety and surrounding environment. Therefore, the wear lining of the side wall needs to be repaired at regular intervals.
However, wear of the wear lining is particularly severe at the slag line portion and the metal line portion as mentioned above. That is to say, wear occurs not uniformly over the entire wear lining but locally. If the wear lining at other portions of side walls is in good condition but the wear lining remaining at the slag line portion or the metal line portion locally decreases in thickness, repair is needed in order to prevent molten metal or slag from leaking out. Therefore, careful inspection and repair of the wear lining are frequently executed in practical operation.
In view of these circumstances, Patent Document 1 discloses that in a blast furnace runner having an inner lining layer formed by casting or spraying an unshaped refractory material, a plurality of precast refractory blocks are combined and placed at a portion of a side wall to be heavily attacked by molten metal or slag flows from a tap hole and thus need to have high fire resistance. This technique aims to reduce wear of a very vulnerable portion of the inner lining layer of the blast furnace runner and allow the entire blast furnace runner to be uniformly worn away, and thus improve durability of the blast furnace runner.
However, since a plurality of precast refractory blocks are combined and placed, the technique of Patent Document 1 requires precast refractory blocks of a plurality of kinds of shapes. In addition, the technique of Patent Document 1 has a risk that the precast refractory blocks may drop off early due to wear of the unshaped refractory material covering peripheries of the combined and placed precast refractory blocks. Therefore, the technique of Patent Document 1 does not fully solve problems such as an increase in production costs caused by the need of precast refractory blocks of a plurality of kinds of shapes and a decrease in service life caused by early drop off of the precast refractory blocks.